This invention relates to a silver halide photographic element containing a combination of a compound that releases a specific type of electron transfer agent (ETARC) and a compound that releases a specific type of development accelerating agent (DARC) for improved photographic imaging. The ETARC compound releases a specific type of electron transfer agent (ETA) and the DARC compound releases a specific type of development accelerating fragment upon reacting with oxidized developing agent.
The sensitivity of widely used silver halide photographic materials has increased over the years from an ISO sensitivity of 100 to an ISO sensitivity of greater than 1000. Emulsions containing large silver halide grains, which give greater sensitivity to light, may be used to increase speed; however, such emulsions usually also increase granularity. In addition, certain silver halide emulsions arc relatively more difficult to develop depending upon their particular physical or chemical properties. For example, silver halide emulsions with large grains or silver halide grains having relatively high iodide content, generally develop at slower rates than emulsions having smaller grains or low iodide content.
Therefore, it is desirable to invent a technique that achieves higher speed with smaller silver halide grains. One way of achieving this is to promote chemical development. Different methods to accelerate development of exposed silver halide grains have been realized.
For example, U.S. Pat. No. 6,110,657 describes the release of improved types of electron transfer agents (ETA)s of limited diffusibility for development acceleration without an increase in xe2x80x98wrong-wayxe2x80x99 interimage. These types of compounds are commonly referred to as electron transfer agent releasing couplers or (ETARC)s. As another example, U.S. Pat. No. 5,605,786 describes a method of imagewise release of an ETA where an xe2x80x94Oxe2x80x94COxe2x80x94(T)nxe2x80x94(ETA) group is attached at the coupling-off site of the ETARC. U.S. Pat. Nos. 4,859,578 and 4,912,025 describe silver halide elements comprising a development inhibitor releasing compound and a compound capable of imagewise releasing an electron transfer agent.
It is also known that couplers that release other types of development accelerating fragments can be used to achieve increased photographic speed. In particular, it is known that compounds that release hydrazine derivatives upon reaction with oxidized developer are effective development accelerator releasing couplers or (DARC)s. For example, U.S. Pat. Nos. 4,482,629; 4,820,616; and 4,618,572 all describe the use of DARCs that release hydrazine derivatives, including those in which the hydrazine derivative also bears a silver absorbable moiety
In spite of all of the efforts in the industry, however, there is still a continuing need for methods of improving the photographic speed of silver halide emulsions without compromising other performance features of the photographic element.
This invention provides a photographic element comprising a support and at least two silver halide emulsion layers and further comprising an electron transfer agent releasing compound represented by formula (I):
CAR1xe2x80x94(L)nxe2x80x94ETAxe2x80x83xe2x80x83(I)
wherein:
CAR1 is a carrier moiety which is capable of releasing xe2x80x94(L)n-ETA on reaction with oxidized developing agent;
L is a divalent linking group, n is 0, 1 or 2; and
ETA is a releasable 1-aryl-3-pyrazolidinone electron transfer agent having a calculated log partition coefficient (c log P) greater than or equal to 2.40 and the total sum of the Hammett sigma(para) values of the substituents on the 1-aryl ring is 0.51 or less, the ETA being bonded to L or CAR1 through either the nitrogen atom in the 2-position or the oxygen attached to the 3-position of the pyrazolidinone ring; and a development accelerator releasing compound represented by formula (II):
CAR1xe2x80x94(SAM)xe2x80x94NX1xe2x80x94NX2X3xe2x80x83xe2x80x83(II)
wherein:
CAR2 is a carrier moiety which is capable of releasing xe2x80x94(SAM)xe2x80x94NX1xe2x80x94NX2X3 on reaction with oxidized developing agent;
SAM is a silver absorbable moiety attached to the carrier moiety and is released on reaction with oxidized development agent; and
xe2x80x94NX1xe2x80x94NX2X3 is a hydrazine group wherein X1, X2 and X3 are individually hydrogen or a substituent chosen from alkyl, aryl, carbonyl, or sulfonyl groups with the proviso that at least one of X1, X2 and X3 is hydrogen.
The photographic elements of this invention exhibit improved photographic speed over that from either the ETARC or DARC alone without compromising other performance features of the photographic element. The improvements in photographic speed in color film elements are unexpectedly synergistic.
The ETARCs utilized in the photographic elements of the invention arc represented by formula (I)
CAR1xe2x80x94(L)nxe2x80x94ETAxe2x80x83xe2x80x83(I)
ETA is a 1-aryl-3-pyrazolidinone derivative having a calculated log partition coefficient (c log P) greater than or equal to 2.40. using MedChem v3.54 (Medicinal Chemistry Project, Pomona College, Claremont, Calif., 1987). The sum total of the Hammett sigma(para) values of all of the substituents on the 1-aryl ring must be 0.51 or less. The ETA is released from xe2x80x94(L)nxe2x80x94 and becomes an active electron transfer agent capable of accelerating development under processing conditions used to obtain the desired dye image.
On reaction with oxidized developing agent during processing, the CAR1 moiety releases the xe2x80x94(L)nxe2x80x94ETA fragment which is capable of releasing an electron transfer agent. The electron transfer agent participates in the color development process to increase the rate of silver halide reduction and color developer oxidation resulting in enhanced detection of exposed silver halide grains and the consequent improved image dye density. If the ETA is too mobile, it can diffuse into other layers from where it was originally released and cause increased development in those layers. This results in wrong-way interimage and a decrease in color saturation and purity. The ETA utilized in the invention has a calculated log partition coefficient (c log P) greater than or equal to 2.40 as described above which reduces mobility. However, in some instances the ETA may not be mobile enough to interact efficiently with the developed silver and developer and hence, it is preferred that the c log P of the ETA fragment be no more than 5.0, or more preferably, no more than 4.0 or most preferably, 3.40 or less. Moreover, if the ETA contains substituents with a sum total of Hamett sigma(para) values of greater than 0.51, then the reduction potential of the ETA fragment becomes too low to interact effectively with silver development and/or developer oxidation.
The electron transfer agent pyrazolidinones that have been found to be useful in providing development increases are derived from compounds generally of the type described in U.S. Pat. Nos. 4,209,580; 4,463,081; 4,471,045; and 4,481,287 and in published Japanese Patent Application Serial No. 62-123172, all incorporated herein by reference. Such compounds comprise a 3-pyrazolidinone structure having an unsubstituted or a substituted aryl group in the 1-position. Preferably these compounds have one or more alkyl groups in the 4- or 5-positions of the pyrazolidinone ring.
Preferred electron transfer agents suitable for use in this invention are represented by structural formulas Ia and Ib: 
R2 and R3 each independently represents hydrogen, a substituted or unsubstituted alkyl group having from 1 to 12 carbon atoms, CH2OR7 or CH2OC(O)R7 where R7 can be a substituted or unsubstituted alkyl, aryl or a heteroatom containing group, CH2SR7, or CH2N(R7a)(R7b) wherein R7a, or R7b each independently represents hydrogen, or a substituted or unsubstituted alkyl or aryl group. When R2 and R3 are alkyl, CH2OR7 or CH2OC(O)R7 groups, and R7 is a substituted or unsubstituted alkyl or aryl group, it is preferred that R2 and R3 comprise from 3 to 8 carbon atoms. When R7 is a heteroatom containing group, it is preferred that R2 and R3 comprise from 4 to 12 carbon atoms. R7 may contain, for example, a morpholino, imidazole, triazole or tetrazole group, or a sulfide or ether linkage.
R4 and R5 each independently represents hydrogen, a substituted or unsubstituted alkyl group having from 1 to 8 carbon atoms, or a substituted or unsubstituted aryl group having from 6 to 10 carbon atoms. Preferably R4 and R5 each represents hydrogen. It is also possible that R3 and R4 may be joined by the necessary atoms to together form a 5- or 6-membered carboxylic or heterocyclic ring system.
R6, which may be present in the ortho, meta or para positions of the aromatic ring, is any substituent which does not interfere with the required log partition coefficient or the functionality of the ETA and meets the requirement that the sum total of all of the Hammett sigma(para) coefficients is 0.51 or less. Hammett sigma(para) values are as described in Substituent Constants for Correlation Analysis in Chemistry and Biology, C. Hansch and A. J. leo, Wiley and Co, New York, 1979. In one embodiment R6 independently represents hydrogen, halogen, a substituted or unsubstituted alkyl group having from 1 to 8 carbon atoms, a substituted or unsubstituted alkoxy group having from 1 to 8 carbon atoms, a substituted or unsubstituted alkylthio group having 1 to 8 carbon atoms, amido (xe2x80x94NHCOxe2x80x94), sulfonamido (xe2x80x94NHSO2xe2x80x94), or a heteroatom containing group or ring. Preferably R6 is hydrogen, halogen, a substituted or unsubstituted alkyl group having from 1 to 8 carbon atoms, or a substituted or unsubstituted alkoxy group having from 1 to 8 carbon atoms. m is 0 to 5. Specific R6 substituents that are not part of this invention are nitro, cyano, sulfonyl, and sulfamoyl (xe2x80x94SO2N less than ). When m is greater than 1, the R6 substituents can be the same or different or can be taken together to form a carbocyclic or heterocyclic ring.
Especially preferred releasable electron transfer agents, suitable for use in this invention are presented in Table I, with R4 and R5 being hydrogen:
The amount of ETARC and DARC that can be employed with this invention can be any concentrations that ire effective for the intended purpose. A possible concentration range for the ETARC is from 6 xcexcmole/m2 to 1000 xcexcmole/m2. A preferred concentration range is 20 xcexcmole/m2 to 140 xcexcmole/m2. A possible concentration range for the DARC is from 0.1 xcexcmole/m2 to 25 xcexcmole/m2. A preferred concentration range is 0.5 mole/m2 to 10 xcexcmole/m2.
The ETA is attached to the coupler at a position that will cause the ETA to be inactive until released. The point of attachment of the ETA to the CAR1 or to the CAR1xe2x80x94(L)nxe2x80x94 linking is through either the nitrogen atom in the 2-position or the oxygen attached to the 3-position of the pyrazolidinone ring as shown for structures Ia or Ib. Such attachment inactivates"" the ETA so that it is unlikely to cause undesirable reactions during storage of the photographic material. However, the oxidized developer formed in an imagewise manner as a consequence of silver halide development reacts with the CAR1 moiety to lead to the cleavage of the bond between the CAR and L. L undergoes further reaction to release the active ETA moiety.
The linking group xe2x80x94Lnxe2x80x94 is employed to provide for controlled release of the ETA moiety from the coupler moiety so that the effect of accelerated silver halide development can be quickly attained. L represents a divalent linking group which is both a good leaving group and which allows release of the ETA without a long delay. n is 0, 1 or 2. Various types of known linking groups can be used. These include quinone methide linking groups such as are disclosed in U.S. Pat. No. 4,409,323; pyrazolonemethide linking groups such as arc disclosed in U.S. Pat. No. 4,421,845; xe2x80x94Oxe2x80x94COxe2x80x94(T)nxe2x80x94 groups such as are disclosed in U.S. Pat. No. 5,605,786, and intramolecular nucleophillic displacement type linking groups such as are disclosed in U.S. Pat. No. 4,248,962. In one suitable embodiment L is a group which forms the following CAR1xe2x80x94(L)nxe2x80x94ETA structures: 
wherein each R8 can independently be hydrogen, a substituted or unsubstituted alkyl group of 1 to 12 carbon atoms or a substituted or unsubstituted aryl group of 6 to 10 carbon atoms. More preferably R8 is a substituted or unsubstituted alkyl group of 1 to 4 carbon atoms. R9 is a substituted or unsubstituted alkyl group of from 1 to 20 carbon atoms, preferably of from 1 to 4 carbon atoms, or a substituted or unsubstituted aryl group of from 6 to 20 carbon atoms, preferably of from 6 to 10 carbon atoms. X is an xe2x80x94NO2, xe2x80x94CN, sulfone, sulfamoyl (i.e., xe2x80x94SO2N less than ), sulfonamido (i.e., xe2x80x94NHSO2xe2x80x94), halogen or alkoxycarbonyl group and p is 0 or 1.
Y represents the atoms necessary to form is a substituted or unsubstituted carbocyclic aromatic ring, or a substituted or unsubstituted heterocyclic aromatic ring. Preferably Y forms a carbocyclic aromatic ring having 6 to 10 carbon atoms or a 5-membered heterocyclic aromatic ring. Suitable heterocyclic rings include pyrazoles, imidazoles, triazoles, pyrazolotriazoles etc. R10 is a substituted or unsubstituted alkyl or aryl group. Z is a carbon or nitrogen atom.
Particularly suitable linking groups are shown by the formulas below: 
wherein Y represents the atoms necessary to form a substituted or unsubstituted phenyl ring, Z is a carbon atom and R9 and p are as defined above. Typical useful linking groups include: 
where R9 is as defined above and p is 0 or 1.
CAR of CAR1 and CAR2 is a carrier moiety that is capable of releasing for ETARCs, the xe2x80x94(L)nxe2x80x94ETA moiety, or in the case of DARCs, the xe2x80x94(SAM)xe2x80x94NX1xe2x80x94NX2X3 moiety, upon reaction with oxidized developing agent. In a preferred embodiment, CAR is a coupler moiety that can release xe2x80x94(L)nxe2x80x94ETA or xe2x80x94(SAM)xe2x80x94NX1xe2x80x94NX2X3 from the coupling site during reaction with oxidized primary amine color developing agent. CAR carriers that are triggered by reaction with oxidized developing agent are capable of releasing a photographically useful group (PUG) and are particularly well known in development inhibitor release (DIR) technology where the PUG is a development inhibitor. Typical references to hydroquinone type carriers are U.S. Pat. Nos. 3,379,529; 3,297,445; and 3,975,395, 4,108,663 discloses similar release from aminophenol and aminonaphthol carriers, while U.S. Pat. No. 4,684,604 features PUG-releasing hydrazide carriers. All of these may be classified as redox-activated carriers for PUG release.
A far greater body of knowledge has been built up over the years on carriers in which a coupler releases a PUG upon condensation with an oxidized primary amine color developing agent. These can be classified as coupling-activated carriers. Representative are U.S. Pat. Nos. 3,148,062; 3,227,554; 3,617,291; 3,265,506; 3,632,345; and 3,660,095.
The coupler from which the electron transfer agent pyrazolidinine moiety or the development accelerator fragment is released includes couplers employed in conventional color-forming photographic processes that yield colored products based on reactions of couplers with oxidized color developing agents. The couplers can also yield colorless products on reaction with oxidized color developing agents. The couplers can also form dyes that are unstable and which decompose into colorless products. Further, the couplers can provide dyes that wash out of the photographic recording materials during processing. Such couplers are well known to those skilled in the art.
The coupler can be unballasted or ballasted with an oil-soluble or fat-tail group. It can be monomeric, or it can form part of a dimeric, oligomeric, or polymeric coupler, in which case more than one ETA moiety or development accelerator fragment can be contained in the ETARC or DARC compound.
Many coupler kinds are known. The dyes formed therefrom generally have their main absorption in the red, green, or blue regions of the visible spectrum. For example, couplers which form clean dyes upon reaction with oxidized color developing agents are described in such representative patents and publications as U.S. Pat. Nos. 2,772,162; 2,895,826; 3,002,836; 3,034,892; 2,474,293; 2,423,730; 2,367,531; 3,041,236; and 4,333,999; and xe2x80x9cFarbkuppler: Eine Literaturubersicht,xe2x80x9d published in Agfa Mitteilungen, Band III, pp. 156-175 (1961). In the coupler structures shown below, the unsatisfied bond indicates the coupling position to which xe2x80x94(L)nxe2x80x94ETA or xe2x80x94(SAM)xe2x80x94NX1xe2x80x94NX2X3 group may be attached.
Preferably such couplers are phenols and naphthols that give cyan dyes on reaction with oxidized color developing agent at the coupling position, i.e., the carbon atom in the 4-position of the phenol or naphthol. Structures of such preferred cyan couplers are: 
where R12 and R13 are individually a ballast group, a hydrogen, a substituted or unsubstituted alkyl or aryl group or a substituted or unsubstituted alkyloxy or aryloxy group, R11 is a halogen atom, an alkyl group having from 1 to 4 carbon atoms or an alkoxy group having from 1 to 4 carbon atoms, and w is 1 or 2. Generally R12 and R13 are groups having less than 20 carbon atoms.
Couplers that form magenta dyes upon reaction with oxidized developing agent are described in such representative patents and publications as U.S. Pat. Nos. 2,600,788; 2,369,489; 2,343,703; 2,311,082; 3,824,250; 3,615,502; 4,076,533; 3,152,896; 3,519,429; 3,062,653; 2,908,573; 4,540,654; and xe2x80x9cFarbkuppler: Eine Literaturubersicht,xe2x80x9d published in Agfa Mitteilungen, Band III, pp. 126-156 (1961).
Preferably, such couplers are pyrazolones and pyrazolotriazoles that form magenta dyes upon reaction with oxidized developing agents at the coupling position, i.e., the carbon atom in the 4-position for pyrazolones and the 7-position for pyrazolotriazoles. Structures of such preferred magenta coupler moieties are: 
wherein R12a and R13a are as defined above for R12 and R13, R13a for pyrazolone structures is typically a phenyl group or a substituted or unsubstituted phenyl group, such as, for example, 2,4,6-trihalophenyl. For the pyrazolotriazole structures R13a is typically alkyl or aryl.
Couplers that form yellow dyes on reaction with oxidized color developing agent are described in such representative patents and publications as U.S. Pat. Nos. 2,875,057; 2,407,210; 3,265,506; 2,298,443; 3,048,194; and 3,447,928; and xe2x80x9cFarbkuppler: Eine Literaturubersicht,xe2x80x9d published in Agfa Mitteilungen, Band III, pp. 112-126 (1961).
Preferably, such yellow dye-forming couplers are acylacetamides, such as benzoylacetanilides and pivalylacetanilides. These couplers react with oxidized developing agent at the coupling position, i.e., the active methylene carbon atom. Structures of such preferred yellow couplers are: 
where R12b and R13b are as defined above for R12 and R13 and can also be alkoxy, alkoxycarbonyl alkanesulfonyl, arenesulfonyl, aryloxycarbonyl, carbonamido, carbamoyl, sulfonamido, or sulfamoyl. R11b is hydrogen or one or more halogen, lower alkyl, (i.e., methyl, ethyl), lower alkoxy (i.e., methoxy, ethoxy), or a ballast (i.e., alkoxy of 16 to 20 carbon atoms) group.
Couplers that form colorless products upon reaction with oxidized color developing agent are described in such representative patents as U.K. Patent No. 861, 138 and U.S. Pat. Nos. 3,632,345; 3,928,041; 3,958,993; and 3,961,959. Preferably, such couplers are cyclic carbonyl containing compounds that form colorless products on reaction with oxidized color developing agent and have the L or xe2x80x94(SAM)xe2x80x94NX1xe2x80x94NX2X3 group attached to the carbon atom in the xcex1-position with respect to the carbonyl group. Structures of such preferred couplers are: 
where R12c is defined as above for R12, and r is 1 or 2.
It will be appreciated, depending on the particular coupler moiety, or the particular developing agent, or the type of processing, the reaction product of the coupler and oxidized color developing agent can be: (1) colored and non-diffusible, in which case it may not be removed during processing from the location where it is formed; (2) colored and diffusible, in which case it may be removed during processing from the location where it is formed or allowed to migrate to a different location; or (3) colorless and diffusible or non-diffusible, in which case it will not contribute to image density.
Especially preferred structures for CARxe2x80x94(L)nxe2x80x94ETA are compounds E-1 through E-19. 
For the development accelerator releasing compound represented by formula (II), SAM is a silver absorbable moiety attached directly to the carrier moiety and is released on reaction with oxidized development agent. A silver absorbable moiety is an atom or group of atoms that is strongly absorbed on silver surfaces. Suitable atoms that arc strongly absorbed to silver are sulfur, selenium, and nitrogen. A preferred atom is sulfur. Suitable groups that are strongly absorbed to silver are nitrogen containing heterocycles with at least on Nxe2x80x94H in its released form according to formula SAM-1 or heterocycles with a free xe2x80x94SH (or its tautomeric equivalent) in its released form according to formula SAM-2. 
where the dashed line represents the atoms necessary to form a heterocyclic ring, * denotes the site of attachment to CAR2 and ** denotes the site of attachment to the hydrazine group. The heterocycles are typically inhibitors of silver development and may be selected from any of the known classes of silver development inhibitors. Among the preferred classes of groups that are strongly absorbed to silver and known to act as inhibitors of silver development are mercaptotetrazoles, mercaptotriazoles, mercaptothiadiazoles, mercaptooxadiazoles, mercaptotetraazaindenes, mercaptobenzoxazines, benzotriazoles, triazoles, tetrazoles, and tetraazaindenes.
It should be appreciated that there may be additional atoms present that chemically link the hydrazine group to the SAM and that the hydrazine group need not be connected directly to the SAM. It is preferred that the spacer atoms be an alkyl, ether, thioether or aryl group with 12 carbon atoms or less, or more preferably, 6 carbon atoms or less. An aryl group is particularly preferred. It should also be appreciated that there may be an optional timing or switch group located between CAR2 and SAM such that when CAR2 reacts with oxidized developer, the timing or switch group is released from CAR2 which then subsequently decomposes and releases the xe2x80x94(SAM)xe2x80x94NX1xe2x80x94NX2X3 group. Any of the appropriate well-known timing or switch groups are appropriate for this use, although it is preferred that a timing or switch group is not present.
Some examples of the SAM fragment including, when appropriate, any additional atoms that connect the SAM to the hydrazine are: 
X1, X2 and X3 are individually hydrogen or a substituent chosen from alkyl, aryl, carbonyl or sulfonyl groups with the proviso that at least one of X1, X2 and X3 is hydrogen. In particular, it is preferred that X1 and X2 are individually hydrogen or an acyl or alkoxycarbonyl group containing 1 to 16 carbon atoms, and more preferably, 1 to 6 carbon atoms. It is most preferred that X1 and X2 are both hydrogen. It is preferred that X3 is an acyl group (xe2x80x94C(xe2x95x90O)xe2x80x94), a thioacyl group (xe2x80x94C(xe2x95x90S)xe2x80x94), a carbamoyl group (xe2x80x94C(xe2x95x90O)N less than ), an alkyloxycarhonyl group (xe2x80x94C(xe2x95x90O)O-alkyl), an aryloxycarbonyl group (xe2x80x94C(xe2x95x90O)O-aryl), an oxalate (xe2x80x94C(xe2x95x90O)xe2x80x94C(xe2x95x90O)xe2x80x94) or oxalate ester (xe2x80x94C(xe2x95x90O)xe2x80x94C(xe2x95x90O)Oxe2x80x94) group, an oxalamido group (xe2x80x94C(xe2x95x90O)xe2x80x94C(xe2x95x90O)N less than ), a sulfonyl group or a sulfamoyl group, each of which may contain 1 to 16 carbon atoms, or more preferably, 1 to 7 carbon atoms. It is most preferred that X3 is a formyl group, an acetyl group, a trifluoroacetyl group, an oxalate or oxalate ester group, a methanesulfonyl group or an arylsulfonyl group.
Some examples of the hydrazine moiety are:
xe2x80x94NHxe2x80x94NHxe2x80x94CHO
xe2x80x94NHxe2x80x94NHxe2x80x94COxe2x80x94CH3 
xe2x80x94NHxe2x80x94NHxe2x80x94COxe2x80x94CF3 
xe2x80x94NHxe2x80x94NHxe2x80x94SO2C3 
xe2x80x94NHxe2x80x94NHxe2x80x94SO2xe2x80x94C6H4-mxe2x80x94CH3 
xe2x80x94N(CHO)xe2x80x94NHxe2x80x94CHO
xe2x80x94NHxe2x80x94NHxe2x80x94CO2C2H5 
xe2x80x94NHxe2x80x94NHxe2x80x94COxe2x80x94NH2 
xe2x80x94NHxe2x80x94NHxe2x80x94COxe2x80x94COxe2x80x94CH3 
xe2x80x94NHxe2x80x94NHxe2x80x94COxe2x80x94COxe2x80x94OCH3 
xe2x80x94NHxe2x80x94NHxe2x80x94COxe2x80x94COxe2x80x94NHC2H5 
Some specific examples of the DARC of the invention are: 
It is desired that the hydrazine of the xe2x80x94(SAM)xe2x80x94NX1xe2x80x94NX2X3 group is inactive until released. Attachment to a ballasted, non-water soluble CAR moiety inactivates the hydrazine so that it is unlikely to cause undesirable reactions during storage of the photographic material. However, the oxidized developer formed in an imagewise manner as a consequence of silver halide development reacts with the CAR2 moiety to lead to the cleavage of the bond between the CAR2 and xe2x80x94(SAM)xe2x80x94NX1xe2x80x94NX2X3. For good storage properties, the DARC compound should be dispersed either as a finely-divided solid particle dispersion or in a high boiling organic solvent as discussed below.
The electron transfer agent releasing coupler compounds of this invention can be prepared according to the methods described in U.S. Pat. Nos. 6,110,657 and 5,605,786. The development accelerator releasing coupler compounds of this invention can be generally prepared according to the methods described in U.S. Pat. Nos. 4,482,629; 4,820,616; and 4,618,572.
A dispersion of ETARC or DARC incorporates the material in a stable, finely divided state in a hydrophobic organic solvent (often referred to as a coupler solvent or permanent solvent) that is stabilized by suitable surfactants and surface active agents usually in combination with a binder or matrix such as gelatin. The dispersion may contain one or more permanent solvents that dissolve the material and maintain it in a liquid state. Some examples of suitable permanent solvents are tricresylphosphate, N,N-diethyllauramide, N,N-dibutyllauramide, p-dodecylphenol, dibutylphthalate, di-n-butyl sebacate, N-n-butylacetanilide, 9-octadecen-1-ol, ortho-methylphenyl benzoate, trioctylamine and 2-ethythexylphosphate. Preferred classes of solvents are carbonamides, phosphates, phenols, alcohols, and esters. When a solvent is present, it is preferred that the weight ratio of compound to solvent be at least 1 to 0.5, or most preferably, at least 1 to 1. Preferred solvents are tricresyl phosphate, N,N-diethyl or N,N-di-n-butyllauramide, di-n-butyl sebacate, p-dodecylphenol, and 2,5-di-t-amylphenol. It is particularly desirable to disperse the ETARC or DARC in the same solvent that is present with the image coupler that is present in the same layer. The dispersion may require an auxiliary coupler solvent initially to dissolve the component, but this is removed afterwards, usually either by evaporation or by washing with additional water. Some examples of suitable auxiliary coupler solvents are ethyl acetate, cyclohexanone, and 2-(2-butoxyethoxy)ethyl acetate. The dispersion may also be stabilized by the addition of polymeric materials to form stable latexes. Examples of suitable polymers for this use generally contain water-solubilizing groups or have regions of high hydrophilicity. Some examples of suitable dispersing agents or surfactants are Alkanol XC or saponin. The materials of the invention may also be dispersed as an admixture with another component of the system such as a coupler or an oxidized developer scavenger so that both are present in the same oil droplet. It is also possible to incorporate the materials of the invention as a solid particle dispersion; that is, a slurry or suspension of finely ground (through mechanical means) compound. These solid particle dispersions may be additionally stabilized with surfactants and/or polymeric materials as known in the art. Also, additional permanent solvent may be added to the solid particle dispersion to help increase activity.
The combination of the specific ETARCs and DARCs of the invention offers enhanced photographic speed. The type of light sensitive silver halide emulsion used in the layer that contains the compound useful in the invention may be important to obtain the desired increase in light sensitivity. The silver halide emulsion is suitably a silver iodobromide emulsion, meaning an emulsion that is low in chloride. By low in chloride, it is meant that there should be no more than 20 mol % chloride. More suitably, there is present in the layer no more than 10 mol % chloride, and typically no more than 1 mol % chloride. The emulsion suitably contains at least 0.01 mol % iodide, or more preferably, at least 0.5 mol % iodide or most preferably, at least 1 mol % iodide. The benefit of the increase in light sensitivity is most apparent in combination with larger sized emulsions that are associated with increased granularity. Thus, it is preferred that the compounds of the invention are used with emulsions that have an equivalent circular diameter of at least 0.6 micrometer, or more preferably, at least 0.8 micrometer, or most preferably, at least 1.0 micrometer. In addition, the benefit of the invention is greatest in origination materials such as color negative or color reversal materials since they require higher sensitivity to light (because of the variable lighting conditions in natural scenes) and low granularity (due to high magnification) relative to color print materials for which exposure conditions are carefully controlled and which are viewed directly under low magnification conditions.
The film elements of the invention must contain at least two light sensitive silver halide layers. It is preferred that the film element contains at least two light sensitive layers that are primarily sensitive to different colors of light. The location of the DARC and ETARC can be in any combination within these layers. For example, the DARC and ETARC can be located in the same layer or in different layers. Preferably, the DARC and ETARC are located in layers sensitive to the same color of light, more preferably, in layers that are adjacent to each other, and most preferably, located in the same layer.
In order to control and maintain granularity over a wide exposure range, it is a common practice to divide an individual color record into separate layers, each containing silver halide emulsions of different degree of sensitivity to the same color of light. While the combination of the invention is most preferred and useful in the most light sensitive layer, it is possible to use the combination in more than one record that is sensitive to the same color of light. For example, in a color record that is split into three layers of different relative sensitivity; fast (F), mid (M) or slow (S), the compounds can be used in each layer only or in any combination; i.e., F+M, F+M+S, F+S, etc. It is not necessary that these layers are adjacent; that is, they may have interlayers or even imaging layers that are sensitive to other colors located between them. In addition, although the most light sensitive layer is typically located in the film structure closest to the exposure source and farthest from the support, the combination of the invention allow for alternative locations of the layers; for example, a more light sensitive layer containing the compounds of the invention may be located below (farther from the exposing source) than a less sensitive layer. It is also possible to use the compounds of the invention in more than one color record at a time.
Moreover, when a number of layers of the same spectral sensitivity but of differing degrees of sensitivity to light are used, it is known that overall granularity can be minimized by using a smaller molar amount of dye-forming coupler than silver in the layers of higher sensitivity. Thus, it is preferred that the light sensitive layer containing the compounds of the invention additionally contain less than a stoichiometric amount of total dye forming coupler(s) relative to the amount of silver contained in the same layer. A suitable molar ratio of dye-forming coupler(s) to silver in the layer containing the compound of the invention would be less than 0.5. Most preferred would be a ratio of 0.2 or even 0.1 or less. In the most extreme case, the ETARC and DARC could be the only coupling species present in the imaging layer.
Unless otherwise specifically stated, substituent groups which may be substituted on molecules herein include any groups, whether substituted or unsubstituted, which do not destroy properties necessary for photographic utility. When the term xe2x80x9cgroupxe2x80x9d is applied to the identification of a substituent containing a substitutable hydrogen, it is intended to encompass not only the substituent""s unsubstituted form, but also its form further substituted with any group or groups as herein mentioned. Suitably, the group may be halogen or may be bonded to the remainder of the molecule by an atom of carbon, silicon, oxygen, nitrogen, phosphorous, or sulfur. The substituent may be, for example, halogen, such as chlorine, bromine or fluorine; nitro; hydroxyl; cyano; carboxyl; or groups which may be further substituted, such as alkyl, including straight or branched chain alkyl, such as methyl, trifluoromethyl, ethyl, t-butyl, 3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such as phenyl, 4-t-butylphenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, such as phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy, and 4-tolyloxy; carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido, alpha-(2,4-di-t-pentyl-phenoxy)acetamido, alpha-(2,4-di-t-pentylphenoxy)butyramido, alpha-(3-pentadecylphenoxy)-hexanamido. alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido, 2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl, N-methyltetradecanamido, N-succinimido, N-phthalimido, 2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, and N-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino, benzyloxycarbonylamino, hexadecyloxycarbonylamino, 2,4-di-t-butylphenoxycarbonylamino, phenylcarbonylamino, 2,5-(di-t-pentylphenyl)carbonylamino, p-dodecyl-phenylcarbonylamino, p-toluylcarbonylamino, N-methylureido, N,N-dimethylureido, N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido, N,N-dioctyl-Nxe2x80x2-ethylureido, N-phenylureido, N,N-diphenylureido, N-phenyl-N-p-toluylureido, N-(m-hexadecylphenyl)ureido, N,N-(2,5-di-t-pentylphenyl)-Nxe2x80x2-ethylureido, and t-butylcarbonamido; sulfonamido, such as metbylsulfonamido, benzenesulfonamido, p-toluylsulfonamido, p-dodecylbenzenesulfonamido, N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino, and hexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl, N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl, N,N-dimethylsulfamoyl; N-[3-(dodecyloxy)propyl]sulfamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl, N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl, such as N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl, N-methly-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such as acetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl, p-dodecyloxyphenoxycarbonyl methoxycarbonyl, butoxycarbonyl, tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl, 3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such as methoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl, 2-ethylhexyloxysulfonyl, phenoxysulfonyl, 2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl, 2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl, phenylsulfonyl, 4-nonylphenylsulfonyl, and p-toluylsulfonyl; sulfonyloxy, such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such as methylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl, hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, and p-toluylsulfinyl; thio, such as ethylthio, octylthio, benzylthio, tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio, 2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such as acetyloxy, benzoyloxy, ocladecanoyloxy, p-dodecylamidobenzoyloxy, N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy; amine, such as phenylanilino, 2-chloroanilino, diethylamine, dodecylamine; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or 3-benzylhydantoinyl; phosphate, such as dimethylphosphate and ethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; a heterocyclic group, a heterocyclic oxy group or a heterocyclic thio group, each of which may be substituted and which contain a 3- to 7-membered heterocyclic ring composed of carbon atoms and at least one hetero atom selected from the group consisting of oxygen, nitrogen and sulfur, such as 2-furyl, 2-thienyl, 2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such as triethylammonium; and silyloxy, such as trimethylsilyloxy.
If desired, the substituents may themselves be further substituted one or more times with the described substituent groups. The particular substituents used may be selected by those skilled in the art to attain the desired photographic properties for a specific application and can include, for example, hydrophobic groups, solubilizing groups, blocking groups, releasing or releasable groups, etc. Generally, the above groups and substituents thereof may include those having up to 48 carbon atoms, typically 1 to 36 carbon atoms and usually less than 24 carbon atoms, but greater numbers are possible depending on the particular substituents selected.
The photographic elements of the invention can be single color elements or multicolor elements. Multicolor elements contain image dye-forming units sensitive to each of the three primary regions of the spectrum. Each unit can comprise a single emulsion layer or multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as known in the art. In an alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer.
A typical multicolor photographic element comprises a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler. The element can contain additional layers, such as filter layers, interlayers, overcoat layers, subbing layers, and the like. The photographic elements of this invention must contain at least two silver halide emulsion layers. The ETARC and DARC compounds are preferably contained in the same silver halide emulsion layer, preferably in the red-sensitive layer, and most preferably, in the most red light sensitive layer.
If desired, the photographic element can be used in conjunction with an applied magnetic layer as described in Research Disclosure, November 1992, Item 34390 published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire PO10 7DQ, ENGLAND, the contents of which are incorporated herein by reference. Further, the photographic elements may have an annealed polyethylene naphthalate film base such as described in Hatsumei Kyoukai Koukai Gihou No. 94-6023, published Mar. 15, 1994 (Patent Office of Japan and Library of Congress of Japan) and maybe utilized in a small format system, such as described in Research Disclosure, June 1994, Item 36230 published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire PO10 7DQ, ENGLAND, and such as the Advanced Photo System, particularly the Kodak ADVANTIX films or cameras.
In the following Table, reference will be made to (1) Research Disclosure, December 1978, Item 17643, (2) Research Disclosure, December 1989, Item 308119, (3) Research Disclosure, September 1994, Item 36544, and (4) Research Disclosure, September 1996, Item 38957, all published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire PO10 7DQ, ENGLAND, the disclosures of which are incorporated herein by reference. The Table and the references cited in the Table are to be read as describing particular components suitable for use in the elements of the invention. The Table and its cited references also describe suitable ways of preparing, exposing, processing and manipulating the elements, and the images contained therein. Photographic elements and methods of processing such elements particularly suitable for use with this invention are described in Research Disclosure, February 1995, Item 37038, published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire PO10 7DQ, ENGLAND, the disclosure of which is incorporated herein by reference.
The photographic elements can be incorporated into exposure structures intended for repeated use or exposure structures intended for limited use, variously referred to as single use cameras, lens with film, or photosensitive material package units.
The presence of hydrogen at the coupling site provides a 4-equivalent coupler, and the presence of another coupling-off group usually provides a 2-equivalent coupler. Representative classes of such coupling-off groups include, for example, chloro, alkoxy, aryloxy, heteroxy, sulfonyloxy, acyloxy, acyl, heterocyclyl, sulfonamido, mercaptotetrazole, benzothiazole, mercaptopropionic acid, phosphonyloxy, arylthio, and arylazo. These coupling-off groups are described in the art, for example, in U.S. Pat. Nos. 2,455,169; 3,227,551; 3,432,521; 3,476,563; 3,617,291; 3,880,661; 4,052,212 and 4,134,766; and in UK. Patents and published application Nos. 1,466,728; 1,531,927; 1,533,039; 2,006,755A and 2,017,704A, the disclosures of which are incorporated herein by reference.
Other image dye-forming couplers may be included in the element such as those image couplers already described above for CAR. In one preferred embodiment a dye forming coupler is contained in the same emulsion layer as the ETARC utilized in this invention. Couplers that form black dyes upon reaction with oxidized color developing agent are described in such representative patents as U.S. Pat. Nos. 1,9:39,231; 2,181,944; 2,333,106; and 4,126,461; German OLS No. 2.644,194 and German OLS No. 2,650,764. Typically, such couplers are resorcinols or m-aminophenols that form black or neutral products on reaction with oxidized color developing agent.
In addition to the foregoing, so-called xe2x80x9cuniversalxe2x80x9d or xe2x80x9cwashoutxe2x80x9d couplers may be employed. These couplers do not contribute to image dye-formation. Thus, for example, a naphthol having an unsubstituted carbamoyl or one substituted with a low molecular weight substituent at the 2- or 3-position may be employed. Couplers of this type are described, for example, in U.S. Pat. Nos. 5,026,628; 5,151,343; and 5,234,800.
It may be useful to use a combination of couplers any of which may contain known ballasts or coupling-off groups such as those described in U.S. Pat. Nos. 4,301,235; 4,853,319; and 4,351,897. The coupler may contain solubilizing groups such as described in U.S. Pat. No. 4,482,629. The coupler may also be used in association with xe2x80x9cwrongxe2x80x9d colored couplers (e.g., to adjust levels of interlayer correction) and, in color negative applications, with masking couplers such as those described in EP 213.490; Japanese Published Application 58-172,647; U.S. Pat. Nos. 2,983,608; 4,070,191; and 4,273,861; German Applications DE 2,706,117 and DE 2,643,965; UK Patent 1,530,272; and Japanese Application 58-113935. The masking couplers may be shifted or blocked, if desired.
The invention materials may be used in association with materials that accelerate or otherwise modify the processing steps, e.g., of bleaching or fixing to improve the quality of the image. Bleach accelerator releasing couplers such as those described in EP 193,389; EP 301,477; U.S. Pat. Nos. 4,163,669; 4,865,956; and 4,923,784, may be useful. Also contemplated is use of the compositions in association with nucleating agents, development accelerators or their precursors (UK Patents 2,097,140 and 2,131,188); electron transfer agents (U.S. Pat. Nos. 4,859,578 and 4,912,025); antifogging and anti color-mixing agents such as derivatives of hydroquinones, aminophenols, amines, gallic acid; catechol; ascorbic acid; hydrazides; sulfonamidophenols; and non color-forming couplers.
The invention materials may also be used in combination with filter dye layers comprising colloidal silver sol or yellow, cyan, and/or magenta filter dyes, either as oil-in-water dispersions, latex dispersions or as solid particle dispersions. Additionally, they may be used with xe2x80x9csmearingxe2x80x9d couplers (e.g., as described in U.S. Pat. No. 4,366,237; 4,420,556; and 4,543,323 and EP 96,570). Also, the compositions may be blocked or coated in protected form as described, for example, in Japanese Application 61/258,249 or U.S. Pat. No. 5,019,492.
The invention materials may further be used in combination with image-modifying compounds such as xe2x80x9cDeveloper Inhibitor-Releasingxe2x80x9d compounds (DIR""s). DIR""s useful in conjunction with the compositions of the invention are known in the art and examples are described in U.S. Pat. Nos. 3,137,578; 3,148,022; 3,148,062; 3,227,554; 3,384,657, 3,379,529; 3,615,506; 3,617,291; 3,620,746; 3,701,783; 3,733,201; 4,049,455; 4,095,984; 4,126,459; 4,149,886; 4,150,228; 4,211,562; 4,248,962; 4,259,437; 4,362,878; 4,409,323; 4,477,563; 4,782,012; 4,962,018; 4,500,634; 4,579,816; 4,607,004; 4,618,571; 4,678,739; 4,746,600; 4,746,601; 4,791,049; 4,857,447; 4,865,959; 4,880,342; 4,886,736; 4,937,179; 4,946,767; 4,948,716; 4,952,485; 4,956,269; 4,959,299; 4,966,835; 4,985,336 as well as in patent publications GB 1,560,240; GB 2,007,662; GB 2,032,914; GB 2,099,167; DE 2,842,063, DE 2,937,127; DE 3,636,824; DE 3,644,416 as well as the following European Patent Publications: 272,573; 335,319; 336,411; 346,899; 362,870; 365,252; 365,346; 373,382; 376,212; 377,463; 378,236; 384,670; 396,486; 401,612; 401,613.
Such compounds are also disclosed in xe2x80x9cDeveloper-Inhibitor-Releasing (DIR) Couplers for Color Photography,xe2x80x9d C. R. Barr, J. R. Thirtle and P. W. Vittum in Photographic Science and Engineering, Vol. 13, p. 174 (1969), incorporated herein by reference. Generally, the developer inhibitor-releasing (DIR) couplers include a coupler moiety and an inhibitor coupling-off moiety (IN). The inhibitor-releasing couplers may be of the time-delayed type (DIAR couplers) which also include a timing moiety or chemical switch which produces a delayed release of inhibitor. Examples of typical inhibitor moieties are: oxazoles, thiazoles, diazoles, triazoles, oxadiazoles, thiadiazoles, oxathiazoles, thiatriazoles, benzotriazoles, tetrazoles, benzimidazoles, indazoles, isoindazoles, mercaptotetrazoles, selenotetrazoles, mercaptobenzothiazoles, selenobenzothiazoles, mercaptobenzoxazoles, selenobenzoxaoles, mercaptobenzimidazoles, selenobenzimidazoles, benzodiazoles, mercaptooxazoles, mercaptothiadiazoles, mercaptothiazoles, mercaptotriazoles, mercaptooxadiazoles, mercaptodiazoles, mercaptooxathiazoles, telleurotetrazoles or benzisodiazoles. In a preferred embodiment, the inhibitor moiety or group is selected from the following formulas: 
wherein RI is selected from the group consisting of straight and branched alkyls of from 1 to about 8 carbon atoms, benzyl, phenyl, and alkoxy groups and such groups containing none, one or more than one such substituent; RII is selected from RI and xe2x80x94SRI; RIII is a straight or branched alkyl group of from 1 to about 5 carbon atoms and m is from 1 to 3; and RIV is selected from the group consisting of hydrogen, halogens and alkoxy, phenyl and carbonamido groups, xe2x80x94COORV and xe2x80x94NHCOORV wherein RV is selected from substituted and unsubstituted alkyl and aryl groups.
Although it is typical that the coupler moiety included in the developer inhibitor-releasing coupler forms an image dye corresponding to the layer in which it is located, it may also form a different color as one associated with a different film layer. It may also be useful that the coupler moiety included in the developer inhibitor-releasing coupler forms colorless products and/or products that wash out of the photographic material during processing (so-called xe2x80x9cuniversalxe2x80x9d couplers).
As mentioned, the developer inhibitor-releasing coupler may include a timing group, which produces the time-delayed release of the inhibitor group such as groups utilizing the cleavage reaction of a hemiacetal (U.S. Pat. No. 4,146,396 and Japanese Applications 60-249148; 60-249149); groups using an intramolecular nucleophilic substitution reaction (U.S. Pat. No. 4,248,962); groups utilizing an electron transfer reaction along a conjugated system (U.S. Pat. Nos. 4,409,323 and 4,421,845 and Japanese Applications 57-188035; 58-98728; 58-209736; 58-209738) groups utilizing ester hydrolysis (German Patent Application (OLS) No. 2,626,315); groups utilizing the cleavage of imino ketals (U.S. Pat. No. 4,546,073); groups that function as a coupler or reducing agent after the coupler reaction (U.S. Pat. Nos. 4,438,193 and 4,618,571) and groups that combine the features describe above. It is typical that the timing group or moiety is of one of the formulas: 
wherein IN is the inhibitor moiety, Zxe2x80x2 is selected from the group consisting of nitro, cyano, alkylsulfonyl; sulfamoyl (xe2x80x94SO2NR2); and sulfonamido (xe2x80x94NRSO2R) groups; n is 0 or 1; and RVI is selected from the group consisting of substituted and unsubstituted alkyl and phenyl groups. The oxygen atom of each timing group is bonded to the coupling-off position of the respective coupler moiety of the DIAR.
Suitable developer inhibitor-releasing couplers for use in the present invention include, but are not limited to, the following: 
It is also contemplated that the concepts of the present invention may be employed to obtain reflection color prints as described in Research Disclosure, November 1979, Item 18716, available from Kenneth Mason Publications, Ltd, Dudley Annex, 12a North Street, Emsworth, Hampshire PO10 7DQ, England, incorporated herein by reference. Materials of the invention may be coated on pH adjusted support as described in U.S. Pat. No. 4,917,994; on a support with reduced oxygen permeability (EP 553,339); with epoxy solvents (EP 164,961); with nickel complex stabilizers (U.S. Pat. Nos. 4,346,165; 4,540,653 and 4,906,559, for example); with ballasted chelating agents such as those in U.S. Pat. No. 4,994,359 to reduce sensitivity to polyvalent cations such as calcium; and with stain reducing compounds such as described in U.S. Pat. No. 5,068,171. Other compounds useful in combination with the invention are disclosed in Japanese Published Applications described in Derwent Abstracts having accession numbers as follows: 90-072,629; 90-072,630; 90072,631; 90-072,632; 90072,633; 90-072,634; 90-077,822; 90-078,229; 90-078,230; 90-079,336; 90-079,337; 90-079,338; 90-079,690; 90-079,691; 90-080,487; 90-080,488; 90-080,489; 90-080,490; 90-080,491; 90-080,492; 90-080,494; 90-085,928; 90-086,669; 90-086,670; 90-087,360; 90-087,361; 90-087,362; 90-087,363; 90-087,364; 90-088,097; 90-093,662; 90-093,663; 90-093,664, 90-093,665; 90-093,666; 90-093,668; 90-094,055; 90-094,056; 90-103,409; 83-62,586; and 83-09,959.
The silver halide emulsions utilized may be of any silver halide composition, including but not limited to silver bromide, silver bromoiodide, silver chlorobromide, and silver chloroiodide. Preferably the silver halide emulsions utilized in this invention arc bromoiodide emulsions.
The silver halide emulsions can contain grains of any size and morphology. Thus, the grains may take the form of cubes, octahedrons, cubo-octahedrons, or any of the other naturally occurring morphologies of cubic lattice type silver halide grains. Further, the grains may be irregular such as spherical grains or tabular grains.
Especially useful in this invention are tabular grain silver halide emulsions. Specifically contemplated tabular grain emulsions are those in which greater than 50 percent of the total projected area of the emulsion grains are accounted for by tabular grains having a thickness of less than 0.3 micrometer (0.5 micrometer for blue sensitive emulsion) and an average tabularity (T) of greater than 25 (preferably greater than 100), where the tern xe2x80x9ctabularityxe2x80x9d is employed in its art recognized usage as
T=ECD/t2
where
ECD is the average equivalent circular diameter of the tabular grains in micrometers and
t is the average thickness in micrometers of the tabular grains.
The average useful ECD of photographic emulsions can range up to about 10 micrometers, although in practice emulsion ECD""s seldom exceed about 4 micrometers. Since both photographic speed and granularity increase with increasing ECD""s, it is generally preferred to employ the smallest tabular grain ECD""s compatible with achieving aim speed requirements.
Emulsion tabularity increases markedly with reductions in tabular grain thickness. It is generally preferred that aim tabular grain projected areas be satisfied by thin (t less than 0.2 micrometer) tabular grains. To achieve the lowest levels of granularity it is preferred that aim tabular grain projected areas be satisfied with ultrathin (t less than 0.06 micrometer) tabular grains. Tabular grain thicknesses typically range down to about 0.02 micrometer. However, still lower tabular grain thicknesses are contemplated. For example, Daubendick et al U.S. Pat. No. 4,672,027 reports a 3 mole percent iodide tabular grain silver bromoiodide emulsion having a grain thickness of 0.017 micrometer. Ultrathin tabular grain high chloride emulsions are disclosed by Maskasky U.S. Pat. No. 5,217,858.
As noted above tabular grains of less than the specified thickness account for at least 50 percent of the total grain projected area of the emulsion. To maximize the advantages of high tabularity, it is generally preferred that tabular grains satisfying the stated thickness criterion account for the highest conveniently attainable percentage of the total grain projected area of the emulsion. For example, in preferred emulsions, tubular grains satisfying the stated thickness criteria above account for at least 70 percent of the total grain projected area. In the highest performance tabular grain emulsions, tabular grains satisfying the thickness criteria above account for at least 90 percent of total grain projected area.
Suitable tabular grain emulsions can be selected from among a variety of conventional teachings, such as those of the following: Research Disclosure, Item 22534, January 1983, published by Kenneth Mason Publications, Ltd., Emsworth, Hampshire PO10 7DD, England; U.S. Pat. Nos. 4,439,520; 4,414,310; 4,433,048; 4,643,966; 4,647,528; 4,665,012; 4,672,027; 4,678,745; 4,693,964; 4,713,320; 4,722,886; 4,755,456; 4,775,617; 4,797,354; 4,801,522; 4,806,461; 4,835,095; 4,853,322; 4,914,014; 4,962,015; 4,985,350; 5,061,069 and 5,061,616.
The combination of ETARC and DARC of the invention is particularly well suited for use with the xe2x80x98low-developabilityxe2x80x99 silver halide emulsions as described in U.S. Pat. No. 5,998,121.
The emulsions utilized in the invention, which are preferably iodobromide, may contain xe2x80x9clow foggingxe2x80x9d silver halide grains, preferably tabular silver halide grains. One definition of a xe2x80x9clow foggingxe2x80x9d emulsion is a fully surface spectrochemically sensitized emulsion with a low xe2x80x98intrinsic fog levelxe2x80x99, defined as the fraction (Dmin-base density) divided by its net maximum density (Dmax-base density). Base density is determined by subjecting samples to a fixing step before the normal color development process. Maximum density is achieved when samples are given sufficient exposure above Dmin such that 0.6 log E less exposure produces less than 6% density reduction. This is measured in a format that is coupler rich, meaning it contains greater than or sufficient coupler on a molar basis that can fully react with the amount of silver halide moles coated per unit area. To demonstrate xe2x80x98normal fogxe2x80x99 vs. xe2x80x98low foggingxe2x80x99 emulsions, an emulsion containing layer may comprise (all values in mg/m2) 430.4 Ag, 4304 mg gelatin, suitable surfactants, and 2 g tetraazaindene/mole of Ag, as well as a color forming coupler. As an example of a yellow record coupler, 1291 mg of Y-1/may be used in the emulsion layer; for a magenta record demonstration, 2077 mg of M-1 may be used and for a cyan record example, 602.6 mg of C-1 may be used. A nominal gel overcoat is typically used, for example, a 2690 mg gelatin overcoat hardened at 1.8% wt/wt hardener to total gelatin in the coating. A nominal time of development of 3xe2x80x215xe2x80x3 in C-41 KODAK Color Negative Developer is used. A fully spectrochemically sensitized emulsion in this definition refers to one or more spectral sensitizing dyes being present that impart either cyan, magenta, or yellow spectral sensitization. Furthermore, the emulsion has been optimally chemically sensitized with a sulfiding agent such as sodium thiosulfate, a gold sensitizing agent such as potassium tetrachloroaurate, a reduction sensitizing agent such as stannous chloride or thiourea dioxide- or any two- or three-way combination of these three classes of chemical sensitizers.
It is known that the different couplers used in the different color records have influence on the extent of development of given silver halide emulsion experiences, such that different xe2x80x98intrinsic fog levelsxe2x80x99 are defined for the different color records. For the blue sensitive or yellow record, an xe2x80x98intrinsic fog levelxe2x80x99 fraction of 0.037 or less distinguishes xe2x80x98low foggingxe2x80x99 emulsions. For the green sensitive record, an xe2x80x98intrinsic fog levelxe2x80x99 of 0.048 or less distinguishes xe2x80x98low foggingxe2x80x99 emulsions. For the red sensitive record, an xe2x80x98intrinsic fog levelxe2x80x99 of 0.034 or less distinguishes xe2x80x98low foggingxe2x80x99 emulsions. It is expected that fully spectrochemically sensitized emulsions used in the most sensitive layers have been optimally sensitized both chemically and spectrally such that their response to light has been maximized at fog levels that are characterized as xe2x80x9cnormalxe2x80x9d or else xe2x80x9clow foggingxe2x80x9d. In addition, emulsions that have not been optimally sensitized to respond to light may meet the low intrinsic fog test, by virtue of being sensitized to achieve other properties such as maximum thermal stability upon extended keeping. These emulsions are also included in the above definition, although they are not normally considered to be fully spectrochemically sensitized.
If an emulsion meets the above definition of xe2x80x9clow foggingxe2x80x9d, it is a xe2x80x9clow fogging emulsionxe2x80x9d regardless of the method of preparation of the emulsion. Another way to define xe2x80x9clow foggingxe2x80x9d is by the method of preparation of the emulsion. Emulsions prepared using the following described methods are considered to be xe2x80x9clow foggingxe2x80x9d whether they meet the above test or not: 1) tabular silver halide grains precipitated in a reaction vessel wherein the majority of the grain growth in the reaction vessel is performed at a pH of less than 4.0 (this includes starch precipitated emulsions as further described and traditional gelatin emulsions) and 2) tabular silver halide grains which have been precipitated in an aqueous medium containing a peptizer that is a water dispersible starch and which have been additionally precipitated in the presence of an oxidizing agent. Preferably the low pH method is utilized with starch precipitated emulsions. These methods will be described in detail below.
The silver halide grains to be used in the invention may be prepared according to methods known in the art, such as those described in Research Disclosure, Item 38957 and James, The Theory of the Photographic Process. These methods generally involve mixing a water soluble silver salt with a water soluble halide salt in the presence of a protective colloid, and controlling the temperature, pAg, pH values, etc., at suitable values during formation of the silver halide by precipitation. In one embodiment of the invention the protective colloid or peptizer is a traditional gelatin peptizer.
In another embodiment of the invention the protective colloid or peptizer is water dispersible, cationic starch. The term xe2x80x9cstarchxe2x80x9d is employed to include both natural starch and modified derivatives, such as dextrinated, hydrolyzed, alkylated, hydroxyalkylated, acetylated, or fractionated starch. The starch can be of any origin, such as cornstarch, wheat starch, potato starch, tapioca starch, sago starch, rice starch, waxy cornstarch, or high amylose cornstarch.
Starches are generally comprised of two structurally distinctive polysaccharides, xcex1-amylose and amylopectin. Both are comprised of xcex1-D-glucopyranose units. In xcex1-amylose the xcex1-glucopyranose units form a 1,4-straight chain polymer. The repealing units take the following form: 
In amylopectin, in addition to the 1,4-bonding of repeating units, 6-position chain branching (at the site of the xe2x80x94CH2OH group above) is also in evidence, resulting in a branched chain polymer. The repeating units of starch and cellulose are diasteroisomers that impart different overall geometries to the molecules. The xcex1-anomer, found in starch and shown in formula I above, results in a polymer that is capable of crystallization and some degree of hydrogen bonding between repeating units in adjacent molecules, but not to the same degree as the xcex2 anomer repeating units of cellulose and cellulose derivatives. Polymer molecules formed by the xcex2 anomers show strong hydrogen bonding between adjacent molecules, resulting in clumps of polymer molecules and a much higher propensity for crystallization. Lacking the alignment of substituents that favors strong intermolecular bonding, found in cellulose repeating units, starch and starch derivatives are much more readily dispersed in water.
The water dispersible starches employed in the practice of the invention are cationicxe2x80x94that is, they contain an overall net positive charge when dispersed in water. Starches are conventionally rendered cationic by attaching a cationic substituent to the xcex1-D-glucopyranose units, usually by esterification or etherification at one or more free hydroxyl sites. Reactive cationogenic reagents typically include a primary, secondary or tertiary amino group (which can be subsequently protonated to a cationic form under the intended conditions of use) or a quaternary ammonium, sulfonium or phosphonium group.
To be useful as a peptizer the cationic starch must be water dispersible. Many starches disperse in water upon heating to temperatures up to boiling for a short time (e.g., 5 to 30 minutes). High sheer mixing also facilitates starch dispersion. The presence of cationic substituents increases the polar character of the starch molecule and facilitates dispersion. The starch molecules preferably achieve at least a colloidal level of dispersion and ideally are dispersed at a molecular levelxe2x80x94i.e., dissolved.
The following teachings illustrate water dispersible cationic starches within the contemplation of the invention:
*Rutenberg et al U.S. Pat. No. 2,989,520;
Meisel U.S. Pat. No. 3,017,294;
Elizer et al U.S. Pat. No. 3,051,700;
Aszolos U.S. Pat. No. 3,077,469;
Elizer et al U.S. Pat. No. 3,136,646;
*Barber et al U.S. Pat. No. 3,219,518;
*Mazzarella et al U.S. Pat. No. 3,320,080;
Black et al U.S. Pat. No. 3,320,118;
Caesar U.S. Pat. No. 3,243,426;
Kirby U.S. Pat. No. 3,336,292;
Jarowenko U.S. Pat. No. 3,354,034;
Caesar U.S. Pat. No. 3,422,087;
*Dishburger et al U.S. Pat. No. 3,467,608;
*Beaninga et al U.S. Pat. No. 3,467,647;
Brown et al U.S. Pat. No. 3,671,310;
Cescato U.S. Pat. No. 3,706,584;
Jarowenko et al U.S. Pat. No. 3,737,370;
*Jarowenko U.S. Pat. No. 3,770,472;
Moser et al U.S. Pat. No. 3,842,005;
Tessler U.S. Pat. No. 4,060,683;
Rankin et al U.S. Pat. No. 4,127,563;
Huchette et al U.S. Pat. No. 4,613,407;
Blixt et al U.S. Pat. No. 4,964,915;
*Tsai et al U.S. Pat. No. 5,227,481; and
*Tsai et al U.S. Pat. No. 5,349,089.
It is preferred to employ an oxidized cationic starch. The starch can be oxidized before (* patents above) or following the addition of cationic substituents. This is accomplished by treating the starch with a strong oxidizing agent. Both hypochlorite (ClOxe2x88x92) or periodate (IO4xe2x88x92) have been extensively used and investigated in the preparation of commercial starch derivatives and preferred. While any convenient oxidizing agent counter ion can be employed, preferred counter ions are those fully compatible with silver halide emulsion preparation, such as alkali and alkaline earth cations, most commonly sodium, potassium, or calcium.
When the oxidizing agent opens the xcex1-D-glucopyranose ring, the oxidation sites are usually at the 2- and 3-position carbon atoms forming the xcex1-D-glucopyranose ring. The 2- and 3-position 
groups are commonly referred to as the glycol groups. The carbon-to-carbon bond between the glycol groups is replaced in the following manner: 
where R represents the atoms completing an aldehyde group or a carboxyl group.
The hypochlorite oxidation of starch is most extensively employed in commercial use. The hypochlorite is used in small quantities to modify impurities in starch. Any modification of the starch at these low levels is minimal, at most affecting only the polymer chain terminating aldehyde groups, rather than the xcex1-D-glucopyranose repeating units themselves. At levels of oxidation that affect the xcex1-D-glucopyranose repeating units the hypochlorite affects the 2-, 3-, and 6-positions, forming aldehyde groups at lower levels of oxidation and carboxyl groups at higher levels of oxidation. Oxidation is conducted at mildly acidic and alkaline pH (e.g.,  greater than 5 to 11). The oxidation reaction is exothermic, requiring cooling of the reaction mixture. Temperatures of less than 45xc2x0 C. are preferably maintained. Using a hypobromite oxidizing agent is known to produce similar results as hypochlorite.
Hypochlorite oxidation is catalyzed by the presence of bromide ions. Since silver halide emulsions are conventionally precipitated in the presence of a stoichiometric excess of the halide to avoid inadvertent silver ion reduction (fogging), it is conventional practice to have bromide ions in the dispersing media of high bromide silver halide emulsions. Thus, it is specifically contemplated to add bromide ion to the starch prior to performing the oxidation step in the concentrations known to be useful in the high bromide {111} tabular grain emulsionsxe2x80x94e.g., up to a pBr of 3.0.
Ceseato U.S. Pat. No. 3,706,584 discloses techniques for the hypochlorite oxidation of cationic starch. Sodium bromite, sodium chlorite, and calcium hypochlorite are named as alternatives to sodium hypochlorite. Further teachings of the hypochlorite oxidation of starches is provided by the following: R. I. Whistler, E. G. Linke and S. Kazeniac, xe2x80x9cAction of Alkaline Hypochlorite on Corn Starch Amylose and Methyl 4-O-Methyl-D-glucopyranosidesxe2x80x9d, Journal Amer. Chem. Soc., Vol. 78, pp. 4704-4709 (1956); R. L. Whistler and R. Schweiger, xe2x80x9cOxidation of Amylopectin with Hypochlorite at Different Hydrogen Ion Concentrations, Journal Amer. Chem. Soc., Vol. 79, pp. 6460-6464 (1957); J. Schmorak, D. Mejzler and M. Lewin, xe2x80x9cA Kinetic Study of the Mild Oxidation of Wheat Starch by Sodium Hypochloride in the Alkaline pH Rangexe2x80x9d, Journal of Polymer Science, Vol. XLIX, pp. 203-216 (1961); J. Schmorak and M. Lewin, xe2x80x9cThe Chemical and Physico-chemical Properties, of Wheat Starch with Alkaline Sodium Hypochloritexe2x80x9d, Journal of Polymer Science: Part A, Vol. 1, pp. 2601-2620 (1963); K. F. Patel, H. U. Mehta and H. C. Srivastava, xe2x80x9cKineties and Mechanism of Oxidation of Starch with Sodium Hypochloritexe2x80x9d, Journal of Applied Polymer Science, Vol. 18, pp. 389-399 (1974); R. L. Whistler, J. N. Bemiller and E. F. Paschall, Starch: Chemistry and Technology, Chapter X, Starch Derivatives: Production and Uses, II. Hypochlorite-Oxidized Starches, pp. 315-323, Academic Press, 1984; and O. B. Wurzburg, Modified Starches: Properties and Uses, III. Oxidized or Hypochlorite-Modified Starches, pp. 23-28 and pp. 245-246, CRC Press (1986). Although hypochlorite oxidation is normally carried out using a soluble salt, the free acid can alternatively be employed, as illustrated by M. E. McKillican and C. B. Purves, xe2x80x9cEstimation of Carboxyl, Aldehyde and Ketone Groups in Hypochlorous Acid Oxystarchesxe2x80x9d, Can. J. Clem., Vol. 312-321 (1954).
Periodate oxidizing agents are of particular interest, since they are known to be highly selective. The periodate oxidizing agents produce starch dialdehydes by the reaction shown in the formula (II) above without significant oxidation at the site of the 6-position carbon atom. Unlike hypochlorite oxidation, periodate oxidation does not produce carboxyl groups and does not produce oxidation at the 6-position. Mehltretter U.S. Pat. No. 3,251,826 discloses the use of periodic acid to produce a starch dialdehydes which is subsequently modified to a cationic form. Mehltretter also discloses for use as oxidizing agents the soluble salts of periodic acid and chlorine. Further teachings of the periodate oxidation of starches is provided by the following: V. C. Barry and P. W. D. Mitchell, xe2x80x9cProperties of Periodate-oxidized Polysaccharides. Part II. The Structure of some Nitrogene-containing Polymersxe2x80x9d, Journal Amer. Chem. Soc., 1953, pp. 3631-3635; P. J. Borchert and J. Mirza, xe2x80x9cCationic Dispersions of Dialdehyde Starch I. Theory and Preparationxe2x80x9d, Tappi, Vol. 47, No. 9, pp. 525-528 (1964); J. E. McCormick, xe2x80x9cProperties of Periodate-oxidized Polysaccharides. Part VII. The Structure of Nitrogen-containing Derivatives as deduced from a Study of Monosaccharide Analoguesxe2x80x9d, Journal Amer. Chem. Soc., pp. 2121-2127 (1966); and O. B. Wurzburg, Modified Starches: Properties and Uses, III. Oxidized or Hypochlorite-Modified Starches, pp. 28-29, CRC Press (1986).
Starch oxidation by electrolysis is disclosed by F. F. Farley and R. M. Hixon, xe2x80x9cOxidation of Raw Starch Granules by Electrolysis in Alkaline Sodium Chloride Solutionxe2x80x9d, Ind. Eng. Chem., Vol. 34, pp. 677-681 (1942).
Depending upon the choice of oxidizing agents employed, one or more soluble salts may be released during the oxidation step. Where the soluble salts correspond to or are similar to those conventionally present during silver halide precipitation, the soluble salts need not be separated from the oxidized starch prior to silver halide precipitation. It is, of course, possible to separate soluble salts from the oxidized cationic starch prior to precipitation using any conventional separation technique. For example, removal of halide ion in excess of that desired to be present during grain precipitation can be undertaken. Simply decanting solute and dissolved salts from oxidized cationic starch particles is a simple alternative. Washing under conditions that do not solubilize the oxidized cationic starch is another preferred option. Even if the oxidized cationic starch is dispersed in a solute during oxidation, it can be separated using conventional ultrafiltration techniques, since there is a large molecular size separation between the oxidized cationic starch and soluble salt by-products of oxidation.
The carboxyl groups formed by oxidation take the form xe2x80x94C(O)OH, but, if desired, the carboxyl groups can, by further treatment, take the form xe2x80x94C(O)ORxe2x80x2, where Rxe2x80x2 represents the atoms forming a salt or ester. Any organic moiety added by esterification preferably contains from 1 to 6 carbon atoms and optimally from 1 to 3 carbon atoms.
The minimum degree of oxidation contemplated is that required to reduce the viscosity of the starch. It is generally accepted (see citations above) that opening an xcex1-D-glucopyranose ring in a starch molecule disrupts the helical configuration of the linear chain of repeating units which in turn reduces viscosity in solution. It is contemplated that at least one xcex1-D-glucopyranose repeating unit per starch polymer, on average, be ring opened in the oxidation process. As few as two or three opened xcex1-D-glucopyranose rings per polymer has a profound effect on the ability of the starch polymer to maintain a linear helical configuration. It is generally preferred that at least 1 percent of the glucopyranose rings be opened by oxidation.
A preferred objective is to reduce the viscosity of the cationic starch by oxidation to less than four times (400 percent of) the viscosity of water at the starch concentrations employed in silver halide precipitation. Although this viscosity reduction objective can be achieved with much lower levels of oxidation, starch oxidations of up to 90 percent of the xcex1-D-glucopyranose repeating units have been reported (Wurzburg, cited above, p. 29). A typical convenient range of oxidation ring-opens from 3 to 50 percent of the xcex1-D-glucopyranose rings.
The water dispersible cationic starch is present during the precipitation (during nucleation and grain growth or during grain growth) of the high bromide tabular grains. Preferably precipitation is conducted by substituting the water dispersible cationic starch for all conventional gelatino-peptizers. In substituting the selected cationic starch peptizer for conventional gelatino-peptizers, the concentrations of the selected peptizer and the point or points of addition can correspond to those employed using gelatino-peptizers.
In addition, it has been unexpectedly discovered that emulsion precipitation can tolerate even higher concentrations of the selected peptizer. For example, it has been observed that all of the selected peptizer required for the preparation of an emulsion through the step of chemical sensitization can be present in the reaction vessel prior to grain nucleation. This has the advantage that no peptizer additions need be interjected after tabular grain precipitation has commenced. It is generally preferred that from 1 to 500 grams (most preferably from 5 to 100 grams) of the selected peptizer per mole of silver to be precipitated be present in the reaction vessel prior to tabular grain nucleation.
At the other extreme it is, of course, well known, as illustrated by Mignot U.S. Pat. No. 1,334,012, that no peptizer is required to be present during grain nucleation and, if desired, addition of the selected peptizer can be deferred until grain growth has progressed to the point that peptizer is actually required to avoid tabular grain agglomeration.
The procedures for high bromide {111} tabular grain emulsion preparation through the completion of tabular grain growth require only the substitution of the selected peptizer for conventional gelatino-peptizers. The following high bromide {111} tabular grain emulsion precipitation procedures are specifically contemplated to be useful in the practice of the invention for the use of gelatin as a peptizer and for the starch peptizer modifications discussed above:
Daubendiek et al U.S. Pat. No. 4,414,310;
Abbott et al U.S. Pat. No. 4,425,426;
Wilgus et al U.S. Pat. No. 4,434,226;
Maskasky U.S. Pat. No. 4,435,501;
Kofron et al U.S. Pat. No. 4,439,520;
Solberg et al U.S. Pat. No. 4,433,048;
Evans et al U.S. Pat. No. 4,504,570;
Yamada et al U.S. Pat. No. 4,647,528;
Daubendick et al U.S. Pat. No. 4,672,027;
Daubendiek et al U.S. Pat. No. 4,693,964;
Sugimoto et al U.S. Pat. No. 4,665,012;
Daubendiek et al U.S. Pat. No. 4,672,027;
Yamada et al U.S. Pat. No. 4,679,745;
Daubendick et al U.S. Pat. No. 4,693,964;
Maskasky U.S. Pat. No. 4,713,320;
Nottorf U.S. Pat. No. 4,722,886;
Sugimoto U.S. Pat. No. 4,755,456;
Goda U.S. Pat. No. 4,775,617;
Saitou et al U.S. Pat. No. 4,797,354;
Ellis U.S. Pat. No. 4,801,522;
Ikeda et al U.S. Pat. No. 4,806,461;
Ohashi et al U.S. Pat. No. 4,835,095;
Makino et al U.S. Pat. No. 4,835,322;
Daubendiek et al U.S. Pat. No. 4,914,014;
Aida et al U.S. Pat. No. 4,962,015;
Ikeda et al U.S. Pat. No. 4,985,350;
Piggin et al U.S. Pat. No. 5,061,609;
Piggin et al U.S. Pat. No. 5,061,616;
Tsaur et al U.S. Pat. No. 5,147,771;
Tsaur et al U.S. Pat. No. 5,147,772;
Tsaur et al U.S. Pat. No. 5,147,773;
Tsaur et al U.S. Pat. No. 5,171,659;
Tsaur et al U.S. Pat. No. 5,210,013;
Antoniades et al U.S. Pat. No. 5,250,403;
Kim et al U.S. Pat. No. 5,272,048;
Delton U.S. Pat. No. 5,310,644;
Chang et al U.S. Pat. No. 5,314,793;
Sutton et al U.S. Pat. No. 5,334,469;
Black et al U.S. Pat. No. 5,334,495;
Chaffee et al U.S. Pat. No. 5,358,840; and
Delton U.S. Pat. No. 5,372,927.
The high bromide tabular grain emulsions, preferably {111} tabular emulsions, that are formed contain at least 50 mole percent, more preferably 70 mole percent bromide, and optimally at least 90 mole percent, based on silver. Silver bromide, silver iodobromide, silver chlorobromide, silver iodochlorobromide, and silver chloroiodobromide tabular grain emulsions are specifically contemplated. Although silver chloride and silver bromide form tabular grains in all proportions, chloride is preferably present in concentrations of 30 mole percent, based on silver, or less. Iodide can be present in the tabular grains up to its solubility limit under the conditions selected for tabular grain precipitation. Under ordinary conditions of precipitation silver iodide can be incorporated into the tabular grains in concentrations ranging up to about 40 mole percent, based on silver. It is generally preferred that the iodide concentration be less than 20 mole percent, based on silver. Typically the iodide concentration is less than 10 mole percent, based on silver, and more preferably less than 6 mole percent, based on silver. To facilitate rapid processing, such as commonly practiced in radiography, it is preferred that the iodide concentration be limited to less than 4 mole percent, based on silver. Significant photographic advantages can be realized with iodide concentrations as low as 0.5 mole percent, based on silver, with an iodide concentration of at least 1 mole percent, based on silver, being preferred.
High bromide {111} tabular grain emulsions precipitated in the presence of a cationic starch are disclosed in the following patents: Maskasky U.S. Pat. Nos. 5,604,085; 5,620,840; 5,667,955; 5,691,131; and 5,733,718.
As noted above, one method of preparing a xe2x80x9clow foggingxe2x80x9d emulsion is wherein the majority (i.e., at least 50 mole percent) of grain growth during emulsion grain precipitation in the reaction vessel, and preferably precipitation of greater than 70 mole % (more preferably greater than 90 mole %) of the emulsion grains based on total silver, is performed at a relatively low pH of less than 4.0, preferably less than or equal to 3.5, more preferably less than or equal to 3.0. This low pH precipitation method may be used with either conventional gelatin peptizers or with starch peptizers. Preferably it is utilized with starch peptizers. While the use of a low pH environment with starch peptizers during grain growth may result in starch hydrolysis leading to the formation of additional aldehyde groups (which are believed to reduce silver ions to generate fog silver centers in emulsion grains), growth of high bromide silver halide emulsion grains at low pH in the presence of a starch peptizer has surprisingly resulted in fewer fog generating grains, even in the absence of use of a strong oxidizing agent during emulsion grain precipitation as was previously thought required to oxidize silver fog centers as they are formed. Maintenance of a low pH environment during grain growth in accordance with the invention is believed to sufficiently suppress the silver ion reduction reaction such that silver centers are not formed at photographically harmful levels, leading to low fog emulsions. As such, in accordance with preferred embodiments of the invention, the addition or generation of strong oxidizing agents in the reaction vessel during grain growth is not needed. While establishing a relatively low pH value is advantageous during grain growth, extremely low pH would be expected to degrade the starch peptizer; therefore, a pH value of at least 1.0 is also preferred. Methods of preparing silver bromide emulsions under low pH conditions are described in U.S. Pat. Nos. 6,383,730 and 6,395,465, the entire disclosures of which are incorporated herein by reference.
The second method of preparing xe2x80x9clow foggingxe2x80x9d emulsions is utilized with starch peptized emulsions. In this method the emulsion is treated with an oxidizing agent, which is capable of oxidizing metallic silver, during or subsequent to grain precipitation. Preferred oxidizing agents are those that in their reduced form have little or no impact on the performance properties of the emulsions in which they are incorporated. Strong oxidizing agents such as those noted above to be useful in oxidizing cationic starch, such as hypochlorite (ClOxe2x88x92) or periodate (IO4xe2x88x92), are specifically contemplated. Specifically preferred oxidizing agents are halogenxe2x80x94e.g., bromine (Br2) or iodine (I2). When bromine or iodine is used as an oxidizing agent, the bromine or iodine is reduced to Brxe2x88x92 or Ixe2x88x92. These halide ions can remain with other excess halide ions in the dispersing medium of the emulsion or be incorporated within the grains without adversely influencing photographic performance. Any level of oxidizing agent can be utilized that is effective in reducing minimum density. Concentrations of oxidizing agent added to the emulsion as low as about 1xc3x9710xe2x88x926 mole per Ag mole are contemplated. Since very low levels of Agxc2x0 are responsible for increases in minimum density, no useful purpose is served by employing oxidizing agent concentrations of greater than 0.1 mole per Ag, mole. A specifically preferred oxidizing agent range is from 1xc3x9710xe2x88x924 to 1xc3x9710xe2x88x922 mole per Ag mole. The silver basis is the total silver at the conclusion of precipitation of the high bromide {111} tabular grain emulsion, regardless of whether the oxidizing agent is added during or after precipitation.
Conventional dopants can be incorporated into the tabular grains during their precipitation, as illustrated by the patents cited above aid Research Disclosure, Item 38957, Section I. Emulsion grains and their preparation, D. Grain modifying conditions and adjustments, paragraphs (3), (4), and (5). It is specifically contemplated to incorporate shallow electron trapping (SET) site providing dopants in the tabular grains, further disclosed in Research Disclosure, Vol. 367, November 1994, Item 36736, and Olm et al U.S. Pat. No. 5,576,171.
It is also recognized that silver salts can be epitaxially grown onto the tabular grains during the precipitation process. Epitaxial deposition onto the edges and/or corners of tabular grains is specifically taught by Maskasky U.S. Pat. No. 4,435,501 and Daubendiek et al U.S. Pat. Nos. 5,573,902 and 5,576,168.
Although epitaxy onto the host tabular grains can itself act as a sensitizer, the emulsions of the invention show sensitivity enhancements with or without epitaxy when chemically sensitized employing one or a combination of noble metal, middle chalcogen (sulfur, selenium and, or tellurium) and reduction chemical sensitization techniques. Conventional chemical sensitizations by these techniques are summarized in Research Disclosure, Item 38957, cited above, Section IV. Chemical sensitizations. It is preferred to employ at least one of noble metal (typically gold) and middle chalcogen (typically sulfur) and, most preferably, a combination of both in preparing the emulsions of the invention for photographic use. The use of a cationic starch peptizer allows distinct advantages relating to chemical sensitization to be realized. Under comparable levels of chemical sensitization higher photographic speeds can be realized using cationic starch peptizers. When comparable photographic speeds are sought, a cationic starch peptizer in the absence of gelatin allows lower levels of chemical sensitizers to be employed and results in better incubation keeping. When chemical sensitizer levels remain unchanged, speeds equal to those obtained using gelatino-peptizers can be achieved at lower precipitation and/or sensitization temperatures, thereby avoiding unwanted grain ripening.
Between emulsion precipitation and chemical sensitization, the step that is preferably completed before any gelatin or gelatin derivative is added to the emulsion, it is conventional practice to wash the emulsions to remove soluble reaction by-products (e.g., alkali and/or alkaline earth cations and nitrate anions). If desired, emulsion washing can be combined with emulsion precipitation, using ultrafiltration during precipitation as taught by Mignot U.S. Pat. No. 4,334,012. Alternatively emulsion washing by diafiltration after precipitation and before chemical sensitization can be undertaken with a semipermeable membrane as illustrated by Research Disclosure, Vol. 102, October 1972, Item 10208; Hagemaier et al Research Disclosure, Vol. 131, March 1975, Item 13122; Bonnet Research Disclosure, Vol. 135, July 1975, Item 13577; Berg et al German OLS 2,436,461 and Bolton U.S. Pat. No. 2,495,918, or by employing an ion-exchange resin, as illustrated by Maley U.S. Pat. No. 3,782,953 and Noble U.S. Pat. No. 2,827,428. In washing by these techniques there is no possibility of removing the selected peptizers, since ion removal is inherently limited to removing much lower molecular weight solute ions.
The emulsions can be surface-sensitive emulsions, i.e., emulsions that form latent images primarily on the surfaces of the silver halide grains, or the emulsions can form internal latent images predominantly in the interior of the silver halide grains. The emulsions can be negative-working emulsions, such as surface-sensitive emulsions or unfogged internal latent image-forming emulsions, or direct-positive emulsions of the unfogged, internal latent image-forming type, which are positive-working when development is conducted with uniform light exposure or in the presence of a nucleating agent.
Photographic elements can be exposed to actinic radiation, typically in the visible region of the spectrum, to form a latent image and can then be processed to form a visible dye image. Processing to form a visible dye image includes the step of contacting the element with a color developing agent to reduce developable silver halide and oxidize the color developing agent. Oxidized color developing agent in turn reacts with the coupler to yield a dye.
With negative-working silver halide, the processing step described above provides a negative image. The described elements can be processed in the known Kodak C-41 color process as described in The British Journal of Photography Annual of 1988, pages 191-198, and other known color negative film processes such as the Kodak ECN-2 process described in the H-24 Manual available from Eastman Kodak Co. Where applicable, the element may be processed in accordance with color print processes such as the RA-4 process of Eastman Kodak Company as described in the British Journal of Photography Annual of 1988, pp. 198-199. Such negative working emulsions are typically sold with instructions to process using a color negative method such as the mentioned C-41, ECN, or RA-4 processes. To provide a positive (or reversal) image, the color development step can be preceded by development with a non-chromogenic developing agent to develop exposed silver halide, but not form dye, and followed by uniformly fogging the element to render unexposed silver halide developable. Such reversal emulsions are typically sold with instructions to process using a color reversal process such as E-6. Alternatively, a direct positive emulsion can be employed to obtain a positive image.
Preferred color developing agents are p-phenylenediamines such as:
4-amino-N,N-(diethylaniline hydrochloride,
4-amino-3-methyl-N,N-diethylaniline hydrochloride,
4-amino-3-methyl-N-ethyl-N-(2-methanesulfonamido-ethyl)aniline sesquisulfate hydrate,
4-amino-3-methyl-N-ethyl-N-(2-hydroxyethyl)aniline sulfate,
4-amino-3-(2-methanesulfonamido-ethyl)-N,N-diethylaniline hydrochloride and
4-amino-N-ethyl-N2-methoxyethyl)-m-toluidine di-p-toluene sulfonic acid.
Development is usually followed by the conventional steps of bleaching, fixing, or bleach-fixing to remove silver or silver halide, washing, and drying.
The following examples are intended to illustrate, but not to limit the invention.